A SF6 tracer study of horizontal mixing in Lake Constance |
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Authors: | Manfred Maiss Johann Ilmberger Axel Zenger Karl Otto Münnich |
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Institution: | (1) Present address: Werderstraße 6a, D-69120 Heidelberg, Germany;(2) Institut für Umweltphysik, University of Heidelberg, Im Neuenheimer Feld 366, D-69120 Heidelberg, Germany |
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Abstract: | Horizontal mixing processes in the hypolimnion of the western part of Lake Constance are studied by measuring the dispersion of a sulfur hexafluoride (SF6) tracer plume. Only 1 liter gaseous SF6 (STP) was released at a central hypolimnic depth of 60 m in August 1990. Over a period of 3 months the horizontal dispersion of the tracer plume was measured by 19 surveys using a new, vertically integrating sampling device. The observed horizontal dispersion is marked by strong storm-induced stirring events. Nevertheless mean turbulent diffusion coefficients for the whole period can be computed. They rise about linear from 0.7 105 cm2/s to 3.0 105 cm2/s with the distance from the western end of the lake. For the hypolimnion of Überlingersee, a sill-separated basin in the western part of Lake Constance, a simple budget model gives an exchange time of 67 ± 6 days with the main basin (Obersee). |
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Keywords: | Horizontal mixing Lake Constance tracer experiment sulfur hexafluoride integrating sampler |
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